1. Technical Field of the Invention
The present invention relates to a honeycomb structure body molding die for extrusion molding a honeycomb structure body.
2. Description of the Related Art
There has been known a honeycomb structure body 8 (see FIG. 6) as a catalyst carrier for carrying a catalyst that purifies exhaust gases emitted from an internal combustion engine of an automotive vehicle or the like. The honeycomb structure body 8 is, for instance, honeycomb-shaped cell walls 81, a large number of cells 82 surrounded with the cell walls 81, and a cylindrical outer circumferential skin 83 covering an outer circumferential sidewall.
In general, the honeycomb structure body 8 is manufactured upon extrusion molding a material including a ceramic raw material by using a honeycomb structure body molding die.
Attempts have heretofore been made in the related art to provide honeycomb structure body molding dies in various structures as disclosed in Japanese Patent Application Publication 2002-283326.
As shown in FIG. 9, for instance, for instance, the honeycomb structure body molding die 91 includes a die main body 92, having material feed bores 931 for feeding the molding material 80, and lattice-shaped slit recesses 941 for squeezing a molding material to form a honeycomb structure body, and a guide ring 95 for guiding the molding material 80, squeezed from the slit recesses 941, to obtain a desired outer profile. Further, the die main body 92 has a stepped section 942 formed in an area radially displaced from the guide ring 95 and protruding in an extruding direction of the molding material 80.
When extrusion molding the material 80 by using the honeycomb structure body molding die 91 of the structure described above, as shown in FIG. 9, the molding material 80 is squeezed from the slit recesses 941 axially facing the guide ring 95 to flow into a clearance 910 between the die main body 92 and the guide ring 95. Then, the molding material 80 flows through the clearance 910 in a direction toward the center of the die main body 92. At a radially inward guide end 951 of the guide ring 95, the stepped section 942 restricts the molding material 80 from further moving intact toward the center of the die main body 92. During such inward movement of the molding material 80, the guide ring 95 guides the molding material 80 to turn the same in the extruding direction such that the honeycomb structure body 8 is formed with an outer circumferential skin 83 made of extruded molding material 80.
As set forth above, almost every part of the material 80 forming the outer circumferential skin 83 is squeezed from the slit recesses 941, held in face-to-face relationship with the guide ring 95, to flow in the extruding direction, upon which the material 80 moves toward the center of the die main body 92. Thereafter, the molding material 80 turns in the extruding direction along an axial direction of the die main body 92.
Meanwhile, the die main body 92 has a slit recess (such a, for instance, a slit recess 949 shown in FIG. 9) opening at a position where the die main body 92 does not axially face the guide ring 95. Thus, the molding material 80 partly contains a material component squeezed from such a slit recess in the extruding direction. The squeezed material component merges with the other component delivered through the clearance. Thus, the squeezed material component and the other component of the molding material 80 are squeezed intact in the extruding direction, thereby forming the outer circumferential skin 83.
That is, the molding material 80 includes one material flow component flowing toward the center of the die main body 92 and the other material flow component squeezed from the slit recess. These material flow components merge with each other in an area in close proximity to the radially inward guide end 951 of the guide ring 95. When this takes place, the material flow components flow in different directions on a stage before these material flow components merge with each other, causing instable moldability of the outer circumferential skin 83. This caused an issue to arise with the occurrence of the outer circumferential skin 83 formed with nonuniform thickness and deteriorated strength.